(1) Field of the Invention
This invention relates to heat exchangers for air conditioning systems, and more particularly it is concerned with a heat exchanger for an air conditioning system which permits heat exchange to take place between a refrigerant flowing through a refigerant passage inside heat tranfer tubes and air flowing outside the heat transfer tubes, or more specifically to a heat exchanger of the type described which enables a high coefficient of overall heat transmission to be achieved by improving the coefficient of heat transfer to and from the air and the coefficient of heat transfer to and from the refrigerant.
(2) Description of the Prior Art
In this type of heat exchanger for an air conditioning system, it is usual practice to use, in combination, heat transfer tubes or smooth tubes which are planar and smooth on inner and outer wall surfaces, and fins secured to outer wall surfaces of the heat transfer tubes. The fins may be flat fins, corrugated or convoluted fins, slitted fins having slits formed in flat fins by pressing-out strips, slitted convoluted fins having slits formed in convoluted fins by pressing-out strips, spine fins, etc. The heat exchangers of the prior art have been developed for the purpose of improving their heat exchange performance by improving the coefficient of heat transfer to and from air which is lower than the coefficient of heat transfer to and from refrigerant.
Any attempt to improve the coefficient of heat transfer to and from air raises the problem that a resistance to the flow of air is increased. Another problem raised is that thermal resistance is increased when the heat given off by the air is transmitted through the heat transfer tubes to the refrigerant. Thus there are limits to the improvements that could be provided to the heat exchange performance by improving the coefficient of overall heat transmission through improvement of the coefficient of heat transfer to and from the air.